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参数资料
| 型号： | LTC1649CS#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 16-SOIC |
| 标准包装： | 50 |
| PWM 型： | 电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 260kHz |
| 占空比： | 93% |
| 电源电压： | 2.7 V ~ 5 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | 0°C ~ 70°C |
| 封装/外壳： | 16-SOIC（0.154"，3.90mm 宽） |
| 包装： | 管件 |
LTC1649
APPLICATIO N S I N FOR M ATIO N
tors that work well in LTC1649 applications. A common
way to lower ESR and raise ripple current capability is to
parallel several capacitors. A typical LTC1649 application
might require an input capacitor with a 5A ripple current
capacity and 2% output shift with a 10A output load step,
which requires a 0.005 ? output capacitor ESR. Sanyo OS-
CON part number 10SA220M (220 μ F/10V) capacitors
feature 2.3A allowable ripple current at 85 ° C and 0.035 ?
ESR; three in parallel at the input and seven at the output
will meet the above requirements.
Input Supply Considerations/Charge Pump
The LTC1649 requires four supply voltages to operate:
V IN , V CC , PV CC1 and PV CC2 . V IN is the primary high power
input, supplying current to the drain of Q1 and the input to
the internal charge pump at the V IN pin. This supply must
be between 2.7V and 6V for the LTC1649 to operate
properly. An internal charge pump uses the voltage at V IN
to generate a regulated 5V output at CP OUT . This charge
pump requires an external 1 μ F capacitor connected be-
tween the C + and C – pins, and an external 10 μ F reservoir
capacitor connected from CP OUT to ground. The voltage at
CP OUT must always be greater than or equal to V IN . If V IN
is expected to rise above 5V, an additional Schottky diode
(D5) should be added from V IN to CP OUT .
CP OUT is typically connected to PV CC2 directly, providing
PV CC2 requires a 10 μ F bypass to ground; this capacitor
can double as the CP OUT reservoir capacitor, allowing a
typical application with CP OUT and PV CC2 connected to-
gether to get away with only a single 10 μ F capacitor at this
node, located close to the PV CC2 pin. V CC can also be
powered from CP OUT , but is somewhat sensitive to noise.
PV CC2 happens to be a significant noisemaker, so most
applications require an RC filter from CP OUT /PV CC2 to V CC .
22 ? and 10 μ F are typical filter values that work well in
most applications.
PV CC1 needs to be boosted to a level higher than CP OUT to
provide gate drive to Q1. The LTC1649 initially used a
charge pump from V IN to create CP OUT ; the typical appli-
cation uses a second charge pump to generate the PV CC1
supply. This second charge pump consists of a Schottky
diode (D CP ) from CP OUT to PV CC1 , and a 1 μ F capacitor
from PV CC1 to the source of Q1. While Q2 is on, the diode
charges the capacitor to CP OUT . When Q1 comes on, its
source rises to V IN , and the cap hauls PV CC1 up to (CP OUT
+ V IN ), adequate to fully turn on Q1. When Q1 turns back
off, PV CC1 drops back down to CP OUT ; fortunately, we’re
not interested in turning Q1 on at this point, so the lower
voltage doesn’t cause problems. The next time Q1 comes
on, PV CC1 bounces back up to (CP OUT + V IN ), keeping Q1
happy. Figure 4 shows a complete power supply circuit for
the LTC1649.
the 5V supply that the G2 driver output uses to drive Q2.
V IN
*OPTIONAL
FOR V IN ≥ 5V
D5*
+
10 μ F
22 ?
+
D CP
10 μ F
1 μ F
+
C IN
C +
V IN
CP OUT
V CC
PV CC2
PV CC1
G1
Q1
L1
1 μ F
CHARGE
PUMP
DRIVE
CIRCUITRY
V OUT
C –
G2
Q2
+
C OUT
10
LTC1649
Figure 4. LTC1649 Power Supplies
1649 F04
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